Why is Complex number notation the way it is?

Steven Majewski sdm7g at Virginia.EDU
Thu Dec 20 00:59:02 CET 2001


On Wed, 19 Dec 2001, Grant Edwards wrote:

> >> I've been coding Python for about a day now, and I can't 'see' why a
> >> complex number like 2+3i is represented as 2+3j in Python.
> >
> > Guido was apparently thinking like an engineer at the
> > time. Electronic engineers use j instead of i to avoid
> > confusion with current.
>
> And I'm sure it's almost as obvious why "i" is used for
> current. :) I was told it was because "c" was already taken for
> capacitance, but I still don't know why "i" was chosen over
> some other as-yet-unused letter.  But, we use notation where
> current flows from "+" to "-" so don't try to confuse us with
> facts!

I think you can blame Ben Franklin for that!

He was the champion of the 'single-fluid' theory of electricity [1]
--  opposed to the dual-fluid theory, which held that the two
poles represented two different electrical fluids which flowed
in opposite directions. Obviously, the positive (+) pole is
where there is a surplus of electrical fluid -- and electricity,
like water, flows from a higher to a lower (negative) level!

Of course, if you've read any book on semiconductor theory, you will
know that Franklin was wrong: the two-fluid theory was the correct
one -- "electrons"  flow in one direction and "holes" flow in the
opposite direction!


-- Steve


[1] I double checked my memory by searching for "Ben Franklin
    electric current fluid" on google and scored  another bullseye:
    <http://sln.fi.edu/tfi/exhibits/franklin.html>







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